The alkanes ethane and pentane, and to a lesser extent certain other aliphatics, in expired breath are biomarkers of lipid peroxidation. It is unlikely that any one specific breath hydrocarbon will be found as a biomarker for a specific disease state. However, a technique that simultaneously measures multiple volatile organic compounds (VOCs) from breath greatly increases the chances that a biomarker profile will be found. The simultaneous measurement of VOCs requires a more comprehensive and precise bioanalytical technique than presently available. The overall goal of Phase I and II is to find an accurate and precise way to measure minute changes in concentrations of VOCs that may accompany an incipient disease state or measure disease activity. The proposed instrumentation would contain 3 modules: (1) a Breath Collection Module which allows collection of 3 L samples of expired breath in less than 5 minutes. Module (II) is a Breath Concentrator and Purifier that is connected to module (III) a Gc-MS instrument, optimized specifically for analysis of the aliphatic hydrocarbons in the Breath Hydrocarbon Profile. This instrument will provide reliable, consistent data on a routine basis with standardized methodology. These three modules will be incorporated into a single complete instrument for use in a clinical laboratory setting. PROPOSED COMMERCIAL APPLICATIONS; A breath gas analyzer would serve as a non-invasive tool to monitor chemical biomarkers for disease prevention, detection of early stages of disease states, or to monitor disease activity. Breath analysis would limit patient stress during sampling and would eliminate drawing of blood samples for diagnosis. An instrument would be constructed to operate in the clinical laboratory setting.